You might be able to find a new flywheel on ebay. But I would save the money and buy a new Predator engine at Harbor Freight, it would be your best bet with your limited knowledge of engines, you can get a 6.5hp for just over $100 and nothing will be wrong with it. Good Luck, take it slow.
Update: Found a small diagram in with the other parts of a piston and and several different side views of rings, I guess this is a diagram for multiple piston types and found a pairing that I think will work
Top Ring: inside bevel faces up
2nd ring: outside bevel faces down
I guess I'm going...